Aqueous acid tin-plating bath

ABSTRACT

AN AQUEOUS ACID TIN-PLATING BATH COMPRISING A SOURCE OF TIN AVAILABLE FOR ELECTRO-PLATING, A SOURCE OF HYDROGEN IONS AND AN ADDITIVE COMPRISING FROM 0.0125% TO 98.7% OF 4,4&#39;&#39;-DI(DIMETHYLAMINO)-DIPHENYLMETHANE AND ONE OR MORE TIN-PLATING ADDITIVES FUNCTIONALLY ACTIVE IN AN ACIDIC TIN-PLATING BATH.

United States Patent vs. cl.- 204-54 R 9 Claims ABSTRACT OF THE DISCLOSURE An aqueous acid tin-plating bath comprising a source of tin available for electro-plating, a source of hydrogen ions and an additive comprising from 0.0125 to 98.7% of 4,4'-di-(dimethylamino)-diphenylmethane and one or more tin-plating additives functionally active in an acidic tin-plating bath. i

increase the :range ofcurrent density over which acceptable plating may .be achieved. Examples of known organic tin-plating additivesinclude condensed sulphonated phenol mixtures described and claimed in British Pat. No. 1,033,662..

However, by means of the incorporation of a tin-plating.

additive known' for use'in acidic baths or a mixture of such additivesa't their knownworking concentrations, acceptable plating-is still only obtained within certain approximate limits of current density, for instance from about 60 'amperes/square foot to about 450 amperes/ square foot. Even at very high levels of addition, acceptable plating cannot be. obtained at high current densities using'known tin-plating additives alone or in admixture.

In the specific case of 4,4'-(dimethylamino)-diphenylmethane, it is possible by the addition of very large amounts of this additive to achieve acceptable plating at very low current density but only at the expense of exceedingits solubility level in the bath and by recourse to the use of high voltages. 1

.We have now discovered thata mixture of 4,4'-di- (dimethylarnino)-diphenylmethane and one or more other tin-plating additives known to be functionally active in acidic tin-plating baths, when addedat a similar level of concentration as conventional additives to an acidic tinplating bath produces surprising synergistic effects resulting in satisfactory plating over a considerably wider range of current densities than can be obtained by the use of any of the additives singly orin other admixture.

Accoringly, the present invention provides a tin-plating additive comprising a proportion within the range of from 0.0125% to 98.7% by weight based on the .total weight of the additive of 4,4'-di-(dimethylamino)-diphenylmethane and one or more tin-plating additives functionally active in an acidic tin-plating bath. The present invention also provides a process in which a tin-plating additive is produced comprising admixing a proportion within the range of from 0.0125% to 98.7%

by weight. of 4,4--di-(dirnethylamino)-diphenylmethane 3,810,824 Patented May 14, 1974 2 and one or more tin-plating additives functionally active in acidic tin-plating baths.

Although the 4,4'-di-(dimethylamino)-diphenylmethane may be employed successfully in high proportions in the tin-plating additive of the present invention, for optimal technical and economic advantage it is preferred not to exceed a proportion of 10% by weight. Thus, if more than 10% by weight of 4,4 di-(dimethylamino)-diphenylmethane is present in the total additive, unacceptable levels of sludge-formation and/or of bath discoloration are observed in the tin-plating bath into which the tinplating additive of the present invention is incorporated. A preferred range of proportions of 4,4'-di-(dimethylamino)-diphenylmethane in the total tin-plating additive is thereforefrom 0.0125 to 10% by weight, from 0.1%

V to 2.0% by weight being particularly preferred.

The second component of the tin-plating additive of the present-invention may beselected from a range of additives known to be functionally active in conventional acidic tin-plating baths, especially the so-called Ferrostan bath, comprising an aqueous solution of stannous tin and phenol sulphonic acid. As examples of suitable additives there may be mentioned the sulphonated phenol additives produced according to the process described and claimed in British Pat. No. 1,033,662; the phenol/polyol condensation products described in co-pending British Pat. No. 1,221,688; sulphonated Bisphenol A-(2:2'-di-pphenylolpropane) in acetic acid solution described in British Pat. No. 1,146,588; an additive consisting essentially of dihydroxydiphenyl sulphone under the trademark Phenolenef; dihydroxydiphenyl sulphone as commercially available; and a commercially available sulphonated ethoxylated .u-naphthol additive.

Preferably the proportion of the second tin-plating additive is within the range of from to 99.9875 by weight, more preferably within the range of from 98% to 99.9% by weight of the total tin-plating additive,

According to the present invention, there is also provided an acidic tin-plating bath comprsin'g a source of tin available for *electro-plating a source of hydrogenions and an additive comprising a proportionwithin the range of from 0.012% to-98.7% by weight of 4;4-di-(dimethyl-- ami-no)diphenylmethane and from 99.9875% to 1.3% by weight of one or more functionally-active tin'-plating"'ad-- ditives." t

It is preferred to usestannous sulphate as thejsource of tinion's. The proportion of tin salt the tin-plating bath is advantageously within the range'of from 1.0% to 20% by weight, more preferably" within the range of from 2.0% to 10% by weight, based on the total weight of the tin-plating bath. 1 1

The proportion of the tin-plating-additive of the presentinvention in the'tin-plating bath maybe, for example,

within the range of from 0.01% to 10% by weight, and preferably within the range of from 0.01% to'5% by weight, based on the total weight of the tin-plating bath.

In addition to the source of tin. ions and the tin plat ing-additive of the present invention, the tin-plating bath desirably contains as the source. of hydrogen ions, phenol sulphonic acid, the source of hydrogen ions preferably being present in a proportion within the range of from 0.1% to 20.0% by weight, "more preferably within the on the.

The present invention is further illustrated by the following examples. Parts and percentages shown therein are by weight unless otherwise stated. Parts by weight bear the same relation to parts by volume as do kilograms to litres.

. 4 As a still further comparative aid, data is presented in Table 1 relating to the plating results achieved when only 4,4'-di- (dimethylamino)-diphenylmethane is employed as the tin-plating additive in the standard Hull test.

TABLE 1 Range of current density over which acceptable plating is achieved (amps/square foot) Current densitiesas v corrected to allow for Band Band Actual hull commercial position width cell current plating line Example Additives present in bath (grams/litre) (cm (cm.) densities conditions Phenolene supra (condensation product of sulphonated o-cresol) 3.3 6.5 68 to 1.5 450 to 64.

DiphoneV (sulphonated BisphenolA derivative) (4.0) 4.6 4.6 45 to 2.0 299 to 86. Dihydroxydiphenylsulphone (6.0) 4.3 5.5 48 to 1.5 330 to 64. Phenol/glucose condensation product (4.0). 4.7 5. 1 45 to 1. Diphone V (2.0) plus Phenolene Supra (2.0 4. 3 5. 5 48 to 1. Phenolene supra (4.0) plus dihydroxydiphenylsulphone (1. 4. 1 5.5 55 to 1. TMADM (0.02).. 5.5 0.0 Nil TMADM (2.0) 4.0 2.0 50 to 1 Phenolene supra (4.0) plus 'IMADM (0.02) 0.2 9. 5 120 to 2... 04 0. 4 9. 1 120 t0 3 (0 06) 0.3 9.7 120 to 4-- enol/glucose condensation product .0) plus TMADM (0.02)..- 0.5 9. 0 120 to 5 Phenolene supra (4.0) plus dihydroxydiphenyl sulphone (1.0) 0.4 9.1 120 to plus TMADM (0.04

EXAMPLES 1-4 What we claim is:

(a) The commercially-available product Phenolene Supra (Phenolene is a registered trademark) which is a. condensation product derived from sulphonated ocresol produced as described in British Pat. No. 1,033,662.

' (b) The commercially-available product Diphone V which is believed to be a sulphonated Bisphenol A derivative and is also believed to be described and claimed in British Pat. No. 1,146,588.

(c) The commercially-available product Phenolene which consists substantially of dihydroxydiphenyl sulphone (Phenolene is a registered trademark).

. (d) A phenol/glycose condensation product described and claimed in our copending British Pat. No. 1,221,688.

250 millilitres of each of the respective solutions were placed in turn in a standard 350 millilitres Hull cell (W. Nohse, the .Hull Cell published R. Draper Limited, 1966) and plating was carried out at 3.0 amps at 50 C. for one minute. The results obtained are summarized in Table 1.

.For the purpose of comparison, data are also included in Table 1 relating to the use of the additives listed under headings (a) to (d) alone, that is, in the absence of 4,4-

relating to the plating results achieved when, as ,the tinplating additive, a mixture of equal partsby weight of additives (a) and (b) listed above is employedin'the standard Hull test.

1. An aqueous acidic tin-plating bath comprising a source of tin available for electroplating, a source of hydrogen ions and from 0.01 to 10% by weight of the tin-plating bath of an additive comprising from 0.0125 to 98.7% by weight of 4,4-di(dimethylamino)-diphenylmethane and from 99.9875 to 1.3% by weight of one or more tin plating additives selected from sulphonated phenol additives produced by sulphonating phenol and/ or cresol with oleum containing 60% to 66% by weight of sulphur trioxide and thereafter heating the resulting sulphonated product for at least one hour without adding further phenol, at a subatmospheric pressure of from S to 25 millimeters of mercury and at a temperature in the range of from C. to C.; the phenol polyol condensation products produced by reacting phenol and an aliphatic polyol containing from 2 to 8 hydroxyl groups per molecule in a 1:1 to 10:1 molar proportions respectfully the condensation reaction being carried out at a temperature of from 50 C. to 250 C.; sulphonated Bisphenol A-(2,2-di-p-phenylolpropane) in acetic acid solution; an additive consisting essentially of dihydroxydiphenyl sulphone and sulphonated ethoxylated ot-naphthol.

2. A tin-plating bath as claimed in claim 1 wherein the proportion of tin salt in the tin-plating bath is within the range of from 1.0% to 20% by weight based on the total weight of the bath. 1

3. A tin-plating bath as claimed in claim 2 wherein the proportion of salt in the tin-plating bath is within the range of from 2.0% to 10% by weight based on the total weight of the bath.

4. A tin-plating bath as claimed in claim 3 wherein the proportion of the tin-plating additive is within the range of from 0.01% to 5% by weight based on the total weight of the tin-plating bath.

5. A tin-plating bath as claimed in claim 1 wherein the proportion of the source of hydrogen ions is within the range of from 0.1% to 20% by weight based on the total weight of the bath.

6. A tin-plating bath as claimed in claim 5 wherein the proportion of the source of hydrogen ions is within the range of from 0.5% to 1 0% by weight based on the total weight of the bath.

- 7. A tin-plating bath as claimed in claim 1 wherein References Cited stannous sulphate is employed ,as the source of tin ions.

' s. A tin-plating bath as claimed in claim 1 wherein the UNITED STfKTES PATENTS source of hydrogen ions is phenol sulphonic acid. 1 8/ 1958 'Frlck et all. 204-54 R 9. A method in which tin-plate is produced comprising 5 3, 3 6/ 1970 Sykes 204-54 R electroplating onto a substrate using a tin-plating 'bath claimed in claim 1. GERALD L. KAPLAN, Primary Examiner 

